1. Field of the Invention
The present invention relates to a method of creating a graded anti-reflective coating (ARC) layer in a single step, and more particularly to a method of modifying the transport properties of an ARC layer with solvents to achieve controlled intermixing with a photo-resist layer.
2. Description of the Related Art
Conventional semiconductor processing involves the application and selective removal of a series of layers, such as light sensitive layers, i.e., photo-resist layers, and anti-reflective coating (ARC) layers, from a semiconductor substrate in a process known as lithography. In general, lithographic processing of a semiconductor substrate involves application of a thin layer of light-sensitive photo-resist to an upper surface of a substrate that is subsequently patterned in order to provide a mask for transferring this pattern to the underlying thin film on a substrate during etching. The patterning of the photo-resist generally involves exposure by a radiation source through a reticle (and associated optics) of the light-sensitive material using, for example, a photo-lithography system, followed by the removal of the irradiated regions of the light-sensitive material (as in the case of positive photo-resist), or non-irradiated regions (as in the case of negative resist) using a developing solvent. Radiation reflected off the layers underlying the photo-resist layer during the exposure step can introduce defects into the pattern. The underlying ARC layer, also referred to as a bottom anti-reflective coating or BARC layer, prevents the reflection of radiation thereby minimizing defects in the pattern of the photo-resist layer. Additionally, minimizing the reflection of radiation during the exposure step can minimize the critical dimension variation of the geometrical features of a photo-resist pattern.
More recently, in order to meet the increasing demand to produce smaller and more complex features, graded ARC layers have been utilized. Graded ARC layers typically consist of a material having non-constant optical parameters throughout the film. One way to approximate a graded ARC is through repeated applications of individual layers of anti-reflective material to form a multi-layer structure wherein each layer has different optical properties. Each anti-reflective layer requires an additional coating step that increases the cost and time associated with semiconductor fabrication. Therefore, a method of producing a graded ARC layer in a minimal number of coating steps would be advantageous.